Imaging devices such as cameras are incorporated into a wide variety of products today. When a camera is mounted on a small-sized electronic apparatus such as a cellular phone or a notebook computer, downsizing of the camera itself is strongly demanded.
An autofocus lens is incorporated into a camera in some cases. In such a case, downsizing of an actuator that displaces the lens is strongly demanded. As a small-sized actuator, an actuator that displaces a movable object by driving a piezoelectric element is known (cf. Patent document 1). Patent document 1 discloses a system in which a leaf spring biases a piezo element so that the piezo element and a shaft member are engaged with each other. Patent document 2 discloses a technique that applies a drive voltage having a given relationship with respect to a resonance frequency of a piezoelectric element under specified conditions.